Good Quote from "The Humane Interface"

Interface designers have tried various approaches to accommodate the premise that users can be separated into beginners and experts. Because this premise is false, the approaches have failed. Adaptive systems that shift automatically from beginner mode to expert mode when they judge that your competence has reached a certain level are a good example. If you are using such a system in beginner mode and it suddenly shifts into expert mode, you will find yourself on unfamiliar ground, at least with regard to a portion of the system. A system that shifts piecemeal, feature by feature, is no better. It will feel unstable and unsettling, because the habits that you were developing as a novice yesterday become useless when the feature shifts into expert mode today.

One web-based program I studied promoted you to expert status after you had used it once successfully. The program put you back into beginner mode when you had not used it for six months. Any such arbitrary schedule may not accord with a user's personal rate of learning and memory decay. If a program that promoted you switches to beginner mode after too short a time, you will feel annoyed at being forced to use the tedious beginner method. If the program does not switch back to beginner mode in time, you will be faced with features that you have forgotten how to use.

-- Jef Raskin